We explore two advantages of interleaving execution with planning. First, the overall planning and execution time can be reduced. Second, information from the environment can be incorporated into the planner's knowledge of the world. We extend the PRODIGY planner to handle execution as prompted by the user and to incorporate information that results from this execution. Such information can either arise automatically or can be input by the user. Finally, we briefly discuss ways to help the user determine potentially useful or needed points for execution during planning.